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Fabricating nano-sized BiVO4/InVO4/g-C3N4 photocatalysts for efficient degradation of Acid Blue 92 azo dye

Posted on 31. August, 2018.

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Photocatalysis using semiconductors has received considerable interest in both the scientific and engineering areas. Especially, metal oxide semiconductor photocatalysts have been widely studied for environmental applications such as cleaning of air and the removal of hazardous compounds from wastewater. 

Metal vanadates are a notable category of inorganic nanomaterials that have received attention due to their wide applications and many researchers has been interested in the synthesis of metal vanadates of manganese, iron, etc. Among several studies of vanadates with suitable activity, bismuth vanadate (BiVO4) has received special attention in recent years, thus Z-scheme overall water splitting and photoelectrochemical water splitting systems based on BiVO4 have been fabricated successfully. There are three crystalline phases reported for BiVO4: tetragonal zircon (z-t), monoclinic scheelite (s-m) and tetragonal scheelite (s-t). BiVO4 has been recognised as a photocatalyst (band gap: 2.4 eV) due to its photocatalytic response to the visible-light region and relatively strong oxidation properties for water purification. In recent years, a number of investigations have been focused on the preparation of indium vanadate (InVO4), which is a small band gap semiconductor with band gap of 2.0 eV. It was used as a novel photocatalyst for photodegradation of contaminants under visible light and water splitting. In recent years, a large variety of coupled systems have been reported such as TiO2/g-C3N4, Ag/BiVO4 and g-C3N4/InVO4. In such coupling, two advantages can be obtained: (1) an improvement in visible light absorption and (2) an increase in the lifetime of the charge carrier. Although the photocatalytic activity of BiVO4 is low, BiVO4/InVO4 nanocomposite is a material with a suitable band gap which can improve light absorption. Graphitic carbon nitride (g-C3N4) is a metalfree semiconductor of medium band gap (2.7 eV) which is non-toxic and thermally stable. In recent years, investigators have synthesised g-C3N4 with simultaneously a porous network and O-doping, by condensation of hydrogen bond-induced melamine–H2O2 supramolecular aggregates. These features have a synergetic effect, thus charge separation and light harvesting are improved. As a novel visible light photocatalyst, it can be added to the heterojunction of BiVO4/InVO4 in order to improve the photocatalytic function. In this study, BiVO4/InVO4 and BiVO4/InVO4/g-C3N4 were synthesised by hydrothermal and ultrasonic-assisted hydrothermal methods respectively. In order to investigate the photocatalytic activity of the prepared samples, several photocatalytic experiments were carried out comparatively using Acid Blue 92 (AB92) under visible light irradiation as a test molecule. AB92, which arises from dye stuff industries, is highly toxic and comparatively more refractory to natural degradation. When a solution of this dye enters the human body, it is split into aromatic amines by liver enzymes and can cause cancers. Thus, the removal of AB92 from wastewaters is essential. Photolysis of AB92 without any photocatalyst under visible light is negligible. Our results demonstrate that the ternary composite (BiVO4/InVO4/g-C3N4) provides excellent photocatalytic activity for AB92 degradation in aqueous solution under visible light irradiation. Approximately 80% of AB92 was degraded after 270 min under the experimental conditions.

Read the full article in Progress in Reaction Kinetics and Mechanism.

DOI: https://doi.org/10.3184/146867818X15161889114493

Authors: Mahboubeh Tasviri* and Samin Bargozideh
Faculty of Chemistry and Petroleum Sciences, Shahid Beheshti University, PO Box 19839-63113, Tehran, Iran
*E-mail: m_tasviri@sbu.ac.ir

Keywords: vanadates, g-C3N4, ternary composites, materials characterisation, photocatalysis, dye degradation

Image: Linear-log plot for AB92 degradation under light irradiation with BiVO4/InVO4 and BiVO4/InVO4/g-C3N4. The inset shows full-range UV-Vis spectra of AB92 at different times.